Improve documentation for `core::fmt` internals
The public interface of `core::fmt` is well-documented, but the internals have very minimal documentation.
do not try fetching the ancestors of errored trait impls
fixes#74483
While building the specialization graph, we use `tcx.all_impls` which discards impls with incorrect self types,
we do however call `trait_def.ancestors` with these impls which caused an ICE as they aren't part of the
specialization graph.
Improve Read::read_exact documentation
Fixes#72186.
For now I simply added a link to `Read::read` and held off changing the text in `Read::read_exact`. I can do it if it is deemed necessary.
@rustbot modify labels: C-enhancement, T-libs
More intra-doc links, add explicit exception list to linkchecker
Fixes the broken links behind #32553
Progress on #32130 and #32129 except for a small number of links. Instead of whitelisting entire files, I've changed the code to whitelist specific links in specific files, and added a comment requesting people explain the reasons they add exceptions. I'm not sure if we should close those issues in favor of the already filed intra-doc link issues.
Add a thumbv4t-none-eabi target
(cc @ketsuban, one of the few other Rust users who programs for GBA.)
---
**EDIT:** This is now a more general `thumbv4t-none-eabi` PR! See [this comment](https://github.com/rust-lang/rust/pull/74419#issuecomment-660391579)
---
Now that the PSP officially has an official target within Rust, well as the lead of the `gba` crate I can't _not_ add a GBA target as well.
I know that the [target tier policy](https://github.com/rust-lang/rfcs/pull/2803) isn't ratified and official, but I'll use it as an outline (cc @joshtriplett):
* Designated Developer: Lokathor
* Naming consistent with any existing targets
* Doesn't create Rust project legal issues.
* No license issues
* Uses the standard Apache/mit license.
* Rust tooling users don't have to accept any new licensing requirements
* Does not support hosting rust tooling.
* Doesn't require linking in proprietary code to obtain a functional binary. However, you will need to do some post-build steps to turn the ELF file into a usable GBA ROM (either for an emulator or for the actual hardware).
* This is a `no_std` environment, without even a standard global allocator, so this adds no new code to `alloc` or `std`.
* The process of building for this target is documented in the `gba` crate ([link](https://rust-console.github.io/gba/development-setup.html)). Well, the docs there are currently a little out of date, they're back on using `cargo-xbuild`, but the crate docs there will get updated once this target is available.
* This places no new burden on any other targets
* Does not break any existing targets.
I'm not fully confident in specifying the same linker script for all possible projects, so I'm currently just not giving a linker script at all, and users can continue to select their own linker script by using `-C` to provide a linker arg.
I added the file, and added it to the `supported_targets!` macro usage, and I think that's all there is to do.
Deny unsafe operations in unsafe functions in libstd/alloc.rs
Partial fix of #73904.
This encloses `unsafe` operations in `unsafe fn` in `libstd/alloc.rs`.
@rustbot modify labels: F-unsafe-block-in-unsafe-fn
ci: Update dist-{i686,x86_64}-linux to Debian 6
This increases the minimum `{i686,x86_64}-unknown-linux-gnu` platform
from RHEL/CentOS 5 (glibc 2.5 and kernel 2.6.18) to a slightly newer
Debian 6 `squeeze` (glibc 2.11 and kernel 2.6.32). While that release is
already EOL, it happens to match the minimum common versions of two
enterprise distros that do still need Rust support -- RHEL 6 (glibc 2.12
and kernel 2.6.32) and SLES 11 SP4 (glibc 2.11 and kernel 3.0).
Closes#62516.
Generating the coverage map
@tmandry @wesleywiser
rustc now generates the coverage map and can support (limited)
coverage report generation, at the function level.
Example commands to generate a coverage report:
```shell
$ BUILD=$HOME/rust/build/x86_64-unknown-linux-gnu
$ $BUILD/stage1/bin/rustc -Zinstrument-coverage \
$HOME/rust/src/test/run-make-fulldeps/instrument-coverage/main.rs
$ LLVM_PROFILE_FILE="main.profraw" ./main
called
$ $BUILD/llvm/bin/llvm-profdata merge -sparse main.profraw -o main.profdata
$ $BUILD/llvm/bin/llvm-cov show --instr-profile=main.profdata main
```
r? @wesleywiser
Rust compiler MCP rust-lang/compiler-team#278
Relevant issue: #34701 - Implement support for LLVMs code coverage instrumentation
Make unreachable_unchecked a const fn
This PR makes `std::hint::unreachable_unchecked` a const fn so we can use it inside a const function.
r? @RalfJung
Fixes#53188.
rustc_metadata: Make crate loading fully speculative
Instead of reporting `span_err`s on the spot crate loading errors are now wrapped into the `CrateError` enum and returned, so they are reported only at the top level `resolve_crate` call, and not reported at all if we are resolving speculatively with `maybe_resolve_crate`.
As a result we can attempt loading crates for error recovery (e.g. import suggestions) without any risk of producing extra errors.
Also, this means better separation between error reporting and actual logic.
Fixes https://github.com/rust-lang/rust/issues/55103
Fixes https://github.com/rust-lang/rust/issues/56590
impl Index<RangeFrom> for CStr
This change implements (partial) slicing for `CStr`.
Since a `CStr` must end in a null byte, it's not possible to trim from the right and still have a valid `CStr`. But, it *is* possible to trim from the left. This lets us be a bit more flexible and treat them more like strings.
```rust
let string = CStr::from_bytes_with_nul(b"Hello World!\0");
let result = CStr::from_bytes_with_nul(b"World!\0");
assert_eq!(&string[6..], result);
```
Document the trait keyword
Partial fix of #34601.
This document the trait keyword. To avoid doing too much and forcing more updates as functionalities evolve, I put two links to the reference, especially for trait objects. This mainly documents the "big" parts, not so much the small details that might trip someone experimenting.
@rustbot modify labels: T-doc,C-enhancement
Add core::task::ready! macro
This PR adds `ready!` as a top-level macro to `libcore` following the implementation of `futures_core::ready`, tracking issue https://github.com/rust-lang/rust/issues/70922. This macro is commonly used when implementing `Future`, `AsyncRead`, `AsyncWrite` and `Stream`. And being only 5 lines, it seems like a useful and straight forward addition to std.
## Example
```rust
use core::task::{Context, Poll};
use core::future::Future;
use core::pin::Pin;
async fn get_num() -> usize {
42
}
pub fn do_poll(cx: &mut Context<'_>) -> Poll<()> {
let mut f = get_num();
let f = unsafe { Pin::new_unchecked(&mut f) };
let num = ready!(f.poll(cx));
// ... use num
Poll::Ready(())
}
```
## Naming
In `async-std` we chose to nest the macro under the `task` module instead of having the macro at the top-level. This is a pattern that currently does not occur in std, mostly due to this not being possible prior to Rust 2018.
This PR proposes to add the `ready` macro as `core::ready`. But another option would be to introduce it as `core::task::ready` since it's really only useful when used in conjunction with `task::{Context, Poll}`.
## Implementation questions
I tried rendering the documentation locally but the macro didn't show up under `core`. I'm not sure if I quite got this right. I used the [`todo!` macro PR](https://github.com/rust-lang/rust/pull/56348/files) as a reference, and our approaches look similar.
## References
- [`futures::ready`](https://docs.rs/futures/0.3.4/futures/macro.ready.html)
- [`async_std::task::ready`](https://docs.rs/async-std/1.5.0/async_std/task/index.html)
- [`futures_core::ready`](https://docs.rs/futures-core/0.3.4/futures_core/macro.ready.html)
std: Switch from libbacktrace to gimli
This commit is a proof-of-concept for switching the standard library's
backtrace symbolication mechanism on most platforms from libbacktrace to
gimli. The standard library's support for `RUST_BACKTRACE=1` requires
in-process parsing of object files and DWARF debug information to
interpret it and print the filename/line number of stack frames as part
of a backtrace.
Historically this support in the standard library has come from a
library called "libbacktrace". The libbacktrace library seems to have
been extracted from gcc at some point and is written in C. We've had a
lot of issues with libbacktrace over time, unfortunately, though. The
library does not appear to be actively maintained since we've had
patches sit for months-to-years without comments. We have discovered a
good number of soundness issues with the library itself, both when
parsing valid DWARF as well as invalid DWARF. This is enough of an issue
that the libs team has previously decided that we cannot feed untrusted
inputs to libbacktrace. This also doesn't take into account the
portability of libbacktrace which has been difficult to manage and
maintain over time. While possible there are lots of exceptions and it's
the main C dependency of the standard library right now.
For years it's been the desire to switch over to a Rust-based solution
for symbolicating backtraces. It's been assumed that we'll be using the
Gimli family of crates for this purpose, which are targeted at safely
and efficiently parsing DWARF debug information. I've been working
recently to shore up the Gimli support in the `backtrace` crate. As of a
few weeks ago the `backtrace` crate, by default, uses Gimli when loaded
from crates.io. This transition has gone well enough that I figured it
was time to start talking seriously about this change to the standard
library.
This commit is a preview of what's probably the best way to integrate
the `backtrace` crate into the standard library with the Gimli feature
turned on. While today it's used as a crates.io dependency, this commit
switches the `backtrace` crate to a submodule of this repository which
will need to be updated manually. This is not done lightly, but is
thought to be the best solution. The primary reason for this is that the
`backtrace` crate needs to do some pretty nontrivial filesystem
interactions to locate debug information. Working without `std::fs` is
not an option, and while it might be possible to do some sort of
trait-based solution when prototyped it was found to be too unergonomic.
Using a submodule allows the `backtrace` crate to build as a submodule
of the `std` crate itself, enabling it to use `std::fs` and such.
Otherwise this adds new dependencies to the standard library. This step
requires extra attention because this means that these crates are now
going to be included with all Rust programs by default. It's important
to note, however, that we're already shipping libbacktrace with all Rust
programs by default and it has a bunch of C code implementing all of
this internally anyway, so we're basically already switching
already-shipping functionality to Rust from C.
* `object` - this crate is used to parse object file headers and
contents. Very low-level support is used from this crate and almost
all of it is disabled. Largely we're just using struct definitions as
well as convenience methods internally to read bytes and such.
* `addr2line` - this is the main meat of the implementation for
symbolication. This crate depends on `gimli` for DWARF parsing and
then provides interfaces needed by the `backtrace` crate to turn an
address into a filename / line number. This crate is actually pretty
small (fits in a single file almost!) and mirrors most of what
`dwarf.c` does for libbacktrace.
* `miniz_oxide` - the libbacktrace crate transparently handles
compressed debug information which is compressed with zlib. This crate
is used to decompress compressed debug sections.
* `gimli` - not actually used directly, but a dependency of `addr2line`.
* `adler32`- not used directly either, but a dependency of
`miniz_oxide`.
The goal of this change is to improve the safety of backtrace
symbolication in the standard library, especially in the face of
possibly malformed DWARF debug information. Even to this day we're still
seeing segfaults in libbacktrace which could possibly become security
vulnerabilities. This change should almost entirely eliminate this
possibility whilc also paving the way forward to adding more features
like split debug information.
Some references for those interested are:
* Original addition of libbacktrace - #12602
* OOM with libbacktrace - #24231
* Backtrace failure due to use of uninitialized value - #28447
* Possibility to feed untrusted data to libbacktrace - #21889
* Soundness fix for libbacktrace - #33729
* Crash in libbacktrace - #39468
* Support for macOS, never merged - ianlancetaylor/libbacktrace#2
* Performance issues with libbacktrace - #29293, #37477
* Update procedure is quite complicated due to how many patches we
need to carry - #50955
* Libbacktrace doesn't work on MinGW with dynamic libs - #71060
* Segfault in libbacktrace on macOS - #71397
Switching to Rust will not make us immune to all of these issues. The
crashes are expected to go away, but correctness and performance may
still have bugs arise. The gimli and `backtrace` crates, however, are
actively maintained unlike libbacktrace, so this should enable us to at
least efficiently apply fixes as situations come up.
---
I want to note that my purpose for creating a PR here is to start a conversation about this. I think that all the various pieces are in place that this is compelling enough that I think this transition should be talked about seriously. There are a number of items which still need to be addressed before actually merging this PR, however:
* [ ] `gimli` needs to be published to crates.io
* [ ] `addr2line` needs a publish
* [ ] `miniz_oxide` needs a publish
* [ ] Tests probably shouldn't recommend the `gimli` crate's traits for implementing
* [ ] The `backtrace` crate's branch changes need to be merged to the master branch (https://github.com/rust-lang/backtrace-rs/pull/349)
* [ ] The support for `libbacktrace` on some platforms needs to be audited to see if we should support more strategies in the gimli implementation - https://github.com/rust-lang/backtrace-rs/issues/325, https://github.com/rust-lang/backtrace-rs/issues/326, https://github.com/rust-lang/backtrace-rs/issues/350, https://github.com/rust-lang/backtrace-rs/issues/351
Most of the merging/publishing I'm not actively pushing on right now. It's a bit wonky for crates to support libstd so I'm holding off on pulling the trigger everywhere until there's a bit more discussion about how to go through with this. Namely https://github.com/rust-lang/backtrace-rs/pull/349 I'm going to hold off merging until we decide to go through with the submodule strategy.
In any case this is a pretty major change, so I suspect that the compiler team is likely going to be interested in this. I don't mean to force changes by dumping a bunch of code by any means. Integration of external crates into the standard library is so difficult I wanted to have a proof-of-concept to review while talking about whether to do this at all (hence the PR), but I'm more than happy to follow any processes needed to merge this. I must admit though that I'm not entirely sure myself at this time what the process would be to decide to merge this, so I'm hoping others can help me figure that out!
Manish Goregaokar
